The present invention relates generally to detection of liquid leakage, and more particularly to liquid leakage detection in which an optical fiber is used to transmit a light beam onto a wall of the object in which leakage is to be detected and to measure the reflected light, thereby inspecting for the presence of liquid leakage.
A high temperature/high pressure liquid is extensively utilized in, for example, nuclear power plants or thermal power plants, where immediate and appropriate measures must be taken when an internal liquid leaks or escapes, otherwise such an internal liquid leakage may lead to serious accidents.
In nuclear power plants, liquid leakage has been detected by continuously monitoring the change of pressure and temperature within a reactor container, as well as the change of radioactivity in the air when a liquid leakage occurred at a pressure boundary in the reactor container.
In the detection of liquid leakage by surveying the change of radioactivity in the air and the pressure and temperature within the reactor container, it is quite difficult to find a premature leak which is very insignificant. Moreover, it is impossible to determine the location of the leakage, although the presence of leakage can be detected.
In one general method of detecting liquid leakage which has been applied extensively in various technical fields, moisture responsive elements are located on the walls of liquid containers and pipes so that changes in humidity are transformed into electrical signals to notify the occurrence of liquid leakage.
That detection method which incorporates liquid leakage sensors such as moisture responsive elements permits local detection of leakages; but application of the moisture responsive elements available at present is limited to temperatures lower than about 150.degree. C. Further, as the liquid leakage which is sensed by the moisture responsive elements is transformed into electrical signals, that inspection system requires cables to transmit electrical signals to an alarm and, accordingly, additional countermeasures are necessary against electrical problems such as electromagnetic induction, short-circuits, sparks, etc.